1. Field of the Invention
The present invention relates to a surface-mount package, a printed circuit board having the package mounted thereon, and a method of inspecting the assembled printed circuit board and package, and more particularly, to a ball grid array package, a printed circuit board having the ball grid array package mounted thereon, and a method of inspecting the assembled printed circuit board and ball grid array package.
2. Description of the Related Art
In recent years, a ball grid array (hereinafter referred to as xe2x80x9cBGAxe2x80x9d) package, which is a key device in high-density mounting technology, has been applied to communications devices such as a portable telephone. Moreover, the BGA package is now starting to be applied to trunk communications devices. It is expected that the BGA package continues to be applied to a wider range of applications as an LSI (Large-Scale Integration) package, to replace the large-sized QFP (Quad Flat Package) with a fine lead pitch.
FIGS. 18(A) and 18(B) schematically show external configurations of a conventional BGA package. FIG. 18(A) is a side view, while FIG. 18(B) is a bottom view. The BGA package 200 has a package body 201 in which semiconductor chips are laminated, and the package body 201 has a bottom thereof formed with a plurality of footprints (pads) 202 on which respective ball-shaped solder bumps 203 are formed on the respective footprints 202.
The BGA package 200 is mounted on a printed circuit board by soldering the solder bumps 203 onto the printed circuit board.
FIG. 19 shows the BGA package 200 mounted on the printed circuit board. The printed circuit board 204 is formed with footprints 205 thereon to which the respective solder bumps 203 are soldered. In order to solder the BGA package 200 onto the printed circuit board 204, similarly to an operation for soldering typical surface-mount components, solder paste 206 is applied onto the respective footprints 205 by a screen printing process, and then the BGA package 200 is placed on the solder paste 206, followed by melting the solder paste 206 and the solder bumps 203 by the use of a heating apparatus.
In general, if the printed circuit board 204 having the BGA package 200 mounted thereon receives a shock e.g. when it is carelessly dropped while being handled, the printed circuit board 204 is distorted, which affects solder joints on the BGA package 200. Each terminal of the BGA package 200 has a larger solder joint area than that of conventional components having leads connected thereto, so that soldered joint strength between the solder bumps 203 and the footprints 205 is relatively high. This prevents the solder bumps 203 and the footprints 205 from breaking away from each other.
However, if joint strength between the package body 201 of the BGA package 200 and the respective footprints 202 or between a substrate surface of the printed circuit board 204 and the respective footprints 205 is low, forces generated by any distortion of the printed circuit board 204 are likely to crack some of the footprints 202, 205 or cause the same to break away from the package body 201 or the printed circuit board 204. Thus, when the printed circuit board 204 receives a shock, the solder bumps 203 in the outermost rows and columns are especially prone to such cracking and breakaway since vibrations, warping, expansion, and/or contraction, have the maximum effect at the edge or peripheral portions of the printed circuit board 204.
To overcome this problem, a method is conventionally employed in which a reinforcing adhesive 207 is applied to the outermost solder bumps 203 and its vicinity, as shown in FIG. 19, so as to securely join the outermost solder bumps 203, the package body 201, and the printed circuit board 204 to each other.
However, this method increases the number of manufacturing steps, resulting in degraded working efficiency. Moreover, when the BGA package 200 is defective, it is required to discard the printed circuit board 204 together with the package 200 rather than simply replace the package 200 with a new one. This results in the waste of materials as well as an increase in manufacturing costs.
Further, since it is impossible to judge by visual inspection whether any of the solder joints on the BGA package 200 is defective, the inspection of electrical connections of the solder joints is conventionally performed at an electronic testing stage of the manufacturing process. However, the conventional electronic test cannot detect either a breakaway or a crack of the footprint 202 or 205 unless there is a disconnection in any pattern connected to the solder bumps 203.
A first object of the present invention is to provide an electronic component package and a printed circuit board which are capable of improving working efficiency in mounting the electronic component package on the printed circuit board, and at the same time preventing a breakaway of footprints formed on the electronic component package for circuit connection.
A second object of the invention is to provide a method of inspecting the printed circuit board, which is capable of detecting a defect, such as a breakaway and a crack, of footprints.
To accomplish the first object, according to a first aspect of the invention, there is provided an electronic component package of ball grid array type. The electronic component package is characterized by comprising a plurality of circuit-connecting bumps formed in a predetermined area, and at least one reinforcing bump formed in an area located outward of the predetermined area, in a manner such that the at least one reinforcing bump is connectable to at least one reinforcing pattern formed on a printed circuit board.
To accomplish the second object, according to a second aspect of the invention, there is provided a method of inspecting a printed circuit board having an electronic component package mounted thereon. This method is characterized by comprising the steps of forming a bridge circuit between reinforcing bumps formed on the electronic component package, and reinforcing footprints formed on the printed circuit board in a manner such that the reinforcing bumps are connected to the reinforcing footprints, and detecting a change in a resistance value of the bridge circuit to thereby detect a defect of the printed circuit board.
The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.